JP7340528B2 - Method for producing microcrystalline cellulose - Google Patents

Description

The present invention relates to a method for producing microcrystalline cellulose (MCC). More particularly, the present invention relates to a comprehensive method for producing MCC that can be further processed.

Microcrystalline cellulose (MCC) is a versatile product in many industrial applications, including pharmaceuticals and food. MCC is also used, for example, in paints, oil drilling, and cosmetics.

Microcrystalline cellulose is a cellulose product in powder form that can be made from any type of natural cellulose. MCC is typically produced using acid hydrolysis of cellulose. International Publication No. 2011/154601 discloses a method of acid hydrolyzing fibrous cellulosic materials to produce microcrystalline cellulose. The temperature is at least 140° C. and the consistency is at least 8% based on the dry weight of cellulose. The amount of acid is small, 0.2-2% based on the dry weight of cellulose. International Publication No. 2011/154600 pamphlet discloses a method for producing microcrystalline cellulose by hydrolyzing fibrous cellulosic material with acid at high temperature. In this document, the production is integrated into the production of the pulp mill such that at least a portion of the chemicals used in the acid hydrolysis are produced by the integrated chemical recovery process of the pulp mill.

In view of known methods, there is a need to develop a comprehensive method for producing microcrystalline cellulose for use as raw material or additive in various applications.

The MCC plant, which produces MCC by acid hydrolysis at high pressure and temperature, can be the process section of a chemical pulp mill. MCC plants can also be stand-alone plants.

A new method is provided for producing microcrystalline cellulose from fibrous cellulosic materials, such as chemical pulp, by acid hydrolysis. With this method,
a) concentrating the suspension of cellulosic material to form a filtrate;
b) adjusting the concentration of the concentrated suspension to 5-40% by adding a diluent and adjusting the pH of the suspension to a value of 4 or less with an acid;
c) increasing the temperature of the suspension to 120-200°C;
d) acid hydrolyzing the pulp suspension at 120-200°C in a reactor to produce a mixture of microcrystalline cellulose and hydrolyzate;
e) discharging the mixture from the reactor to low pressure and low temperature to flash the mixture and produce a flash stream;
f) processing the mixture to separate the microcrystalline cellulose from the hydrolyzate, washing the separated microcrystalline cellulose in one or more washing devices, and g) concentrating for further processing. The concentration of microcrystalline cellulose is increased by concentration and drying for further processing.

Fibrous cellulosic materials may be derived from woody plant materials such as conifers or hardwoods. Preferred fibrous cellulosic materials are bleached or unbleached chemical pulps, such as kraft pulp, soda AQ pulp, sulfite pulp, neutral sulfite pulp, acid sulfite pulp or organosolv pulp. The pulp may be a pulp obtained immediately after cooking, a pulp that has been oxygen delignified after cooking, or a pulp that has been oxygen delignified and bleached. Preferred pulps are oxygen delignified pulps and/or fully bleached pulps. Dissolving pulp is a good raw material because of its high cellulose content. It is also possible to use fibrous cellulosic materials obtained from non-wood lignocellulosic plant materials such as cotton, grass, bagasse, straw from cereal crops, flax, hemp, sisal, abaca or bamboo. The fibrous cellulosic material, such as chemical pulp, preferably has a lignin content of less than 40 kappa numbers, more preferably less than 30 kappa numbers, and most preferably less than 10 kappa numbers.

The first step of the new method, step a), is a pre-concentration stage. By concentrating the feed pulp to a higher concentration, it is easier to obtain various unavoidable diluents (dilute sulfuric acid, condensate from direct steam heating, weak hydrolysates, etc.) required by later steps of the method. Therefore, the desired concentration can be maintained during the hydrolysis stage. Without pre-concentration and subsequent dilution, the filtrates formed in the post-hydrolysis process stages are less used and at least a portion of these filtrates must be discharged as waste water. Typically, these filtrates are formed in the wash stage of the MCC. According to the invention, these filtrates can be used for dilution after concentration, and the filtrates can be recycled in the process. The concentration may be carried out using a screw press or other known dewatering equipment suitable for pulp suspensions, such as drum filters, disc filters, filter presses, belt presses, twin wire presses, dewatering presses, wash presses. I can do it. If the MCC plant is integrated into a pulp mill producing feed pulp, some or all of the filtrate of the pre-concentration stage can be recovered and transferred to the chemical pulp mill. Filtrate recovery improves water economics for MCC plants and pulp mills. The filtrate can be used in pulp bleaching or brown storage areas.

After the pre-concentration stage, the pulp concentration of the hydrolysis reactor is controlled by dilution. The diluent can be weak hydrolyzate from washing the microcrystalline cellulose, condensate from the heat recovery system of the MCC plant, strong hydrolyzate separated from the microcrystalline cellulose after the hydrolysis reactor, or process water. It's good. Weak hydrolysates are formed when microcrystalline cellulose is processed in one or more washers and the filtrate is separated. When the mixture from the hydrolysis reactor is discharged to a lower pressure and temperature, for example to a blow tube, flash steam is produced and the flash steam is transferred to a condenser for recovery of heat to hot water. Condensate is also produced when microcrystalline cellulose is dried, whereby steam is formed and heat is recovered to hot water in a drying condenser. The process water may be hot water heated in the condenser of the MCC plant.

Dilution after pre-concentration may be carried out, for example on a screw conveyor, as the pulp is transferred from the pre-concentration stage towards the hydrolysis reactor. If necessary, the diluent can be heated, for example by direct steam injection. The dilution screw drops the pulp into a standpipe from which it is pumped forward at a consistency of 5-40%, preferably 10-30%, typically by a medium consistency (MC) pump or screw pump.

The pulp suspension is then pumped towards a hydrolysis reactor. The pulp is acidified by injecting acid into the pulp after or before the feed pump. Pulp temperature is increased by one or more direct steam injection devices, such as the steam injection heater described in US Pat. No. 6,361,025. Medium pressure steam from a pulp mill boiler plant is typically used as a heat source for direct steam heating. In stand-alone MCC plants, steam is supplied from an external source.

Uniformly mix the acid and steam into the pulp suspension using a mixer. Using a feed pump, optionally using for example a booster pump, the pulp pressure is increased to a reactor pressure which is typically between 3 and 14 bar (g) at the top of the reactor.

The acid can be an organic or inorganic acid. Typically the acid is sulfuric acid. Sulfuric acid can be produced in a pulp mill. A non-chlorine-containing acidic liquid stream, such as bleach filtrate from a pulp mill, can also be used to acidify the pulp suspension. In stand-alone MCC plants, acid is supplied from an external source.

The hydrolysis is carried out in the liquid phase in a reactor under acidic conditions (pH 4.0 or less, preferably 2-3) at high temperatures of 120-200°C, typically 120-185°C, preferably 150-170°C. It will be held in A mixture of microcrystalline cellulose and hydrolyzate is formed during a residence time in the reactor of 30 seconds to 240 minutes, typically 5 to 240 minutes, preferably 10 to 60 minutes. During hydrolysis, the amorphous cellulose structure and hemicellulose are dissolved and the cellulose fibers are converted into particles with an average diameter of about 10-200 μm.

The reactor is typically a vertical vessel, which can be an up-flow or down-flow reactor.

The microcrystalline cellulose and hydrolyzate mixture is blown from the reactor to lower pressure and temperature. The mixture is typically discharged into a blow tube where it is flashed to a lower temperature and pressure. The generated flash steam is condensed in a condenser. The condensate can be used diluted or transferred to a chemical pulp mill for use there.

After blowing, the mixture is treated to separate the hydrolyzate from the microcrystalline cellulose. Before separation, the mixture is diluted, for example at the bottom of the blow tube, and then the mixture is pumped forward.

The diluent can be weak hydrolyzate from the wash section, condensate from the drying condenser or process water.

The diluent can be cooled in a cooler to reduce the temperature of the mixture to a level suitable for subsequent washing sections. The mixture is pumped forward to the first washer at a suitable feed concentration, such as 3-10%. Separation of the hydrolyzate from microcrystalline cellulose is performed in the first washing device. Separation may take place in a concentrator before the first washing device.

Washing of the hydrolysis product is performed using one or more washing devices. The cleaning principle can be dilution-concentration or displacement cleaning, depending on the type of device. The cleaning machine can be any type of equipment suitable for particulate materials, such as drum cleaning machines, centrifuges, disc filters, drum filters, filter presses, belt presses, twin wire presses, screw presses, wash presses or belt cleaning machines. Something can happen.

Washing is done in countercurrent. The cleanest wash liquid is fed to the final wash stage and the filtrate from each wash stage is transferred countercurrently in the direction of the MCC flow to the previous wash stage.

If pre-dilution by washing is required for the washer(s), the pre-dilution is carried out using the filtrate of the subsequent washer, the condensate from the drying condenser and/or the process water. In the first washer, predilution may take place in the blow tube. In subsequent washers, predilution takes place in the repulsion screw conveyor of the preceding washer. A repulper after the first washer drops the diluted final product into a standpipe and pumps the product from the standpipe to a subsequent washer, typically at a concentration of 3-10%.

In displacement cleaning, the cleaning liquid may be the filtrate of the subsequent washer, the condensate from the drying condenser and/or the process water.

The hydrolyzate is separated from the MCC in a first washer. Hydrolysates are rich in carbohydrates, are typically neutralized, and can be used to produce energy or bioproducts. A portion of the hydrolyzate can be recycled to the pulp suspension for pH adjustment prior to hydrolysis. It can also be recycled to the hydrolysis reactor.

The filtrate or filtrates (weak hydrolyzate) from the subsequent washers can be used as wash and/or diluent in the MCC wash or as diluent after the pre-concentration stage. Weak hydrolysates may also be used for pulp concentration control or pH adjustment before and/or within the hydrolysis reactor.

The final device of the washing section operates only as a washer or as a concentrator which adjusts the concentration of the product to a suitable level depending on the subsequent dryer. It is beneficial for the drying energy consumption that the concentration of the product is high before drying, preferably above 40%, typically 40-50%. Optionally, the MCC can be transferred directly to next processing or use after concentration if drying is not required or if a concentration of 40-50% is preferred in the next process stage.

Further processing or uses include industrial applications such as pharmaceutical, food, cosmetics, paper and board applications, and the production of derivatives of microcrystalline cellulose such as nanocellulose and CMC.

The next step in the process may be drying if the MCC needs to be dried to a high dry content before further processing or use. The type of dryer can be a paddle dryer, a flash dryer, a fluidized bed dryer, a belt dryer, a drum dryer, a spiral dryer, a plate dryer or a spray dryer. Dryers utilize power systems such as chemical pulp mill steam, electricity, and typically low or medium pressure steam. As the product progresses through the dryer, its water evaporates and is discharged to the condenser. The condensate can be utilized in the MCC production line or transferred to a chemical pulp mill. In a stand-alone MCC plant, the dryer utilizes a power system, such as steam or electricity from an external utility supplier.

Typically, the dried product with a concentration above 93% is transferred from the dryer(s) to subsequent product processing, such as a packaging step.

Acidic liquid streams from MCC production that are not needed in the MCC plant can be transferred to the pulp mill. These streams include hydrolyzate and filtrate from pre-concentration, washing and/or concentration. The acidic liquid can be used in pre-hydrolyzed kraft pulp production, the acid stage of pulp bleaching and/or the acidification stage in tall oil plants. Condensate from flushing or drying can also be used in pulp mills.

In order to enable a better understanding of the invention and to illustrate the manner in which it may be carried out, reference is now made, by way of example only, to the accompanying drawings, in which: FIG.

1 is a schematic diagram showing an exemplary system for carrying out the method according to the invention; FIG.

FIG. 1 shows an exemplary system of an MCC plant that can be used in accordance with the present invention. In this embodiment, the MCC plant is integrated into a chemical pulp mill. The new method can also be implemented in stand-alone MCC plants.

In the initial stage of the new process, fibrous cellulosic material is fed through line 1 to pre-concentration stage 2. The material may be derived from woody plant materials such as conifers or hardwoods. Preferred fibrous cellulosic materials are bleached or unbleached chemical pulps, such as kraft pulps, or dissolving pulps.

The concentration may be carried out using a screw press or other known dewatering equipment suitable for pulp suspensions, such as drum filters, disc filters, filter presses, belt presses, twin wire presses, dewatering presses, wash presses. I can do it. If the MCC plant is integrated into a pulp mill, some or all of the filtrate from the concentration stage can be recovered and transferred via line 3 to the chemical pulp mill. The filtrate can be used in pulp bleaching or brown storage areas.

After concentration stage 2, the pulp concentration of acid hydrolysis is controlled by dilution. The pulp is guided through a line 4 in which a diluent is added to the pulp, which is further sent to a dilution screw 5. The diluent may include condensate from the heat recovery system of the MCC plant. Dilution can be carried out, for example on a screw conveyor, when the pulp is transferred from the pre-concentration stage towards the hydrolysis reactor. The dilution screw drops the pulp into a standpipe 6 from which it is pumped forward at a concentration of 5 to 40%, preferably 10 to 30%, by a pump 8, for example a medium consistency (MC) pump or a screw pump. Ru.

Next, the pulp suspension is pumped toward the hydrolysis reactor 12 . The pulp is acidified by injecting acid 7 into the pulp after or before the feed pump 8. The pulp temperature is increased by one or more direct steam injection devices 9, such as the steam injection device heater described in US Pat. No. 6,361,025. The steam is typically medium pressure steam 10. A mixer 11 is used to uniformly mix acid and steam into the pulp suspension. Using the feed pump 8, if necessary, for example using a booster pump, the pulp pressure is increased to a reactor pressure which is typically between 3 and 12 bar (g) at the top of the reactor.

The acid can be an organic or inorganic acid. Typically the acid is sulfuric acid. Sulfuric acid can be produced in a pulp mill. Acidic liquid streams such as bleach filtrate from a pulp mill can also be used to acidify the pulp suspension.

The hydrolysis is carried out in the reactor 12 under acidic conditions (pH 4.0 or less, preferably 2-3) and at high temperature (120-200°C, typically 120-185°C, preferably 150-170°C). be exposed. During a residence time in reactor 12 of 5 to 240 minutes, typically 10 to 60 minutes, a mixture of microcrystalline cellulose and hydrolyzate is formed.

Reactor 12 is typically a vertical vessel that can be an up-flow or down-flow reactor.

The microcrystalline cellulose and hydrolyzate mixture is blown from reactor 12 to lower pressure and temperature. The mixture is typically discharged through line 13 into a blow tube 14 where it flashes to a lower temperature and pressure. The generated flash steam 33 is condensed in a condenser 35 to generate hot water 34. The condensate can be transferred via lines 36 and 38 to the pulp diluent in line 4 or via line 37 to a chemical pulp mill where it can be utilized.

After blowing, the mixture is treated to separate the hydrolyzate from the microcrystalline cellulose. The mixture is first diluted, for example at the bottom of the blow tube 14, and then the mixture is pumped forward.

The diluent may be weak hydrolyzate 44 from the wash section, condensate from the drying condenser or process water.

The diluted liquid can be cooled in a cooler 43 to reduce the temperature of the mixed liquid to a level suitable for the subsequent washing section. The mixture is pumped forward through line 15 to first washer 16 at a suitable feed concentration, such as 3-10%. The hydrolysis products are easily fluidized and suspended even at moderate concentrations, allowing the use of process pumps.

Washing of the hydrolysis product is performed using one or more washing devices. The washing principle is dilution concentration or displacement washing. In this embodiment, a dilution concentration method is used. Washers 16 and 18 may be drum washers.

Washing is done in countercurrent. The cleanest wash liquid, such as hot water, is fed from line 20 to the final wash or concentration stage 21, and the filtrates 47 and 42 from wash/concentration stages 21 and 18 are transported countercurrently in the direction of the MCC flow to the previous wash stage. do.

The washing device concentrates the product to a concentration of 25-30% and discharges it into a subsequent repulse screw conveyor washer or into a drying section.

If the cleaning requires pre-dilution for the washer(s), the pre-dilution is carried out using the filtrate of the subsequent washer, the condensate from the drying condenser and/or the process water. . In the first washer, predilution may take place in the blow tube. In subsequent washers, predilution takes place in the repulse screw conveyor of the preceding washer. The repulper after the first washer drops the diluted final product into a standpipe and pumps the product from the standpipe to the subsequent washer, typically at a concentration of 3-10%.

In displacement cleaning, the cleaning liquid may be the filtrate of the subsequent washer, the condensate from the drying condenser and/or the process water.

The hydrolyzate is separated from the MCC in the first washer 16. The hydrolyzate is rich in carbohydrates and can be used for energy production in the pulp mill, where the hydrolyzate is transported through lines 39,41. A portion of the hydrolyzate can be recycled into the pulp suspension through line 40 for pH adjustment prior to hydrolysis in reactor 12. It can also be recycled directly to the hydrolysis reactor.

The filtrate (weak hydrolyzate) from the second washer 18 may be used as a diluent in the screw conveyor 5, to which the filtrate is transferred via line 46. The filtrate may be heated directly with steam heater 48 . The filtrate from the second washer may also be added to the hydrolysis reactor 12 via line 45.

The final device 21 of the washing section operates only as a washer or as a concentrator which adjusts the dry concentration of the MCC product to a suitable level depending on the subsequent dryer. It is beneficial for the drying energy consumption that the concentration of the product is high before drying, preferably above 40%, typically 40-50%.

If the MCC needs to be dried to a high dry content before further processing or use, the next step in the process is drying. The type of dryer can be a paddle dryer, a flash dryer, a fluidized bed dryer, a belt dryer, a drum dryer, a spiral dryer, a plate dryer or a spray dryer. Dryer 23 utilizes a power system, such as chemical pulp mill steam, electricity, typically low or medium pressure steam 24 . This steam is condensed in a dryer 23, and the condensate 26 is returned to the boiler plant to be used as boiler water. As the product progresses through the dryer, its moisture evaporates and is discharged through line 27 to condenser 29 where hot water 28 is produced. The condensate in lines 30, 31 is utilized in pulp dilution in line 4 or is transferred to a chemical pulp mill via line 32. Typically, the dried product with a concentration above 93% is transferred from the dryers 23-25 to subsequent product processing, such as a packaging step.

Optionally, if drying is not required, the MCC can be transferred directly to next processing or use after concentration to a concentration of 40-50%.

Claims (10)

A method for producing microcrystalline cellulose from fibrous cellulosic material by acid hydrolysis in a microcrystalline cellulose (MCC) plant, the method comprising:
a) concentrating the suspension of cellulosic material to form a filtrate;
b) adjusting the concentration of the concentrated suspension to 5-40% by adding a diluent, and adjusting the pH of the suspension to a value of 4 or less with an acid;
c) increasing the temperature of the suspension to 150-200 °C;
d) acid hydrolyzing the suspension at 150-200 °C in a reactor to produce a mixture of microcrystalline cellulose and hydrolyzate;
e) discharging the mixture from the reactor to low pressure and low temperature to flash the mixture and produce flash steam;
f) processing said mixture to separate microcrystalline cellulose from the hydrolyzate, washing said separated cellulose in one or more washing devices, and g) concentrating for further processing. or increasing the concentration of microcrystalline cellulose by concentrating and drying for further processing. 2. The diluent according to claim 1, characterized in that the diluent in step b) comprises a weak hydrolyzate from the washing of microcrystalline cellulose and/or a condensate from the heat recovery system of the MCC plant. the method of. 3. Method according to claim 1 or 2, characterized in that the flash vapor from step e) is transferred to a condenser so that a condensate for use in step b) is formed. 4. Process according to claim 1, 2 or 3, characterized in that the MCC plant is integrated into the pulp production of a pulp mill. 5. According to claim 4, characterized in that the filtrate formed in the concentration of the suspension of cellulosic material in step a) is recovered and transferred to the pulp mill, where it is used for pulp processing. the method of. Claim 4, characterized in that the acid hydrolyzate and/or acid filtrate from step f) is used in pre-hydrolyzed kraft pulp production, in the acid stage of pulp bleaching or in the tall oil plant of the pulp mill. Or the method described in 5. Process according to any one of claims 1 to 6, characterized in that the temperature of the hydrolysis in step d) is between 150 and 185°C, preferably between 150 and 170°C. Claim characterized in that in step g) the concentration of the microcrystalline cellulose is increased to 40-50% by concentration and the concentrated MCC is transferred from the MCC plant to further processing without drying. The method according to any one of Items 1 to 7. Process according to any one of claims 1 to 7, characterized in that in step g) the concentration of the microcrystalline cellulose is increased by concentration and drying to a dry content of at least 93%. In step f), the mixture is diluted before the separation of the microcrystalline cellulose from the hydrolyzate, and the weak hydrolyzate from the washing of the microcrystalline cellulose is used as diluent. , the method according to any one of claims 1 to 9.